Why do some people exposed to coronavirus get sick and others don't?

TORONTO --
One of the most perplexing parts of the coronavirus pandemic has been the fact that some people become seriously sick with the virus while their closest loved ones remain healthy and, in some cases, test negative.

It was announced on March 25 that Prince Charles tested positive for COVID-19 while his wife, Camilla, tested negative. In Canada, Prime Minister Justin Trudeau showed no symptoms of the virus despite Sophie Gregoire Trudeau suffering from a fever and other uncomfortable symptoms.

The question of why some people fall ill and others don’t is one that researchers are working to answer. But one of the likeliest factors is the health of our individual immune systems.

“So you might have a stronger immune system that makes you less susceptible to becoming infected or that makes you more resistant to the infection,” Dr. Eleanor Fish, an immunology professor at the University of Toronto, told CTVNews.ca in a phone interview on Wednesday.

Everyone’s immune system reacts differently when exposed to a virus. Someone with a strong, healthy immune system who is exposed to a virus may not become infected, or may become infected but show few symptoms. Those with compromised immune systems and the elderly are considered at higher risk of dying from COVID-19.

Some doctors have suggested that Trudeau may already have the coronavirus but has no symptoms. Trudeau has not been tested for the virus, as most doctors recommend against testing people who are asymptomatic.

In Camilla’s case, Dr. Fish said it’s possible that proper hygiene could’ve played a role in her negative test results. However, she added that it’s entirely possible that Camilla could test positive later.

“There are many examples of families where one individual becomes infected and … with proper hand washing, not touching their nose and mouth, you can actually prevent transmission within a family,” she said.

Recent data suggest that men are more likely to become infected with the coronavirus than women. Dr. Fish attributes this trend to the fact that women generally have a much more robust immune response to infections.

“And that makes sense because females carry, they’re the one who carry the fetus, so they need to be protected,” she said. “So we shouldn’t be too surprised that there are more males than females becoming infected.”

It’s important to understand that, just because someone doesn’t test positive for the coronavirus or show symptoms, does not mean they are somehow immune. At this point, little is known about immunity, though experts do believe people who recover from the virus experience a period of immunity. Precisely how long that immunity may last is still unknown.

“What does it meant to be immune? It means you’ve had to be exposed to the virus once before. And this is a newly emerging virus infection,” Dr. Fish said.

Experts anticipate it could take at least a year for a vaccine to be developed and properly tested. Until then, one of the best things people can do on an individual level is maintain proper hygiene and eat a healthy, balanced diet.

There are no foods or vitamins that can prevent a person from getting the coronavirus — or any virus, for that matter — but the immune system can be bolstered by eating vitamin-rich fruits and vegetables, according to Priyanka Mishra, a postdoctoral research associate with Simon Fraser University.

“Indirectly, they help,” Mishra told CTVNews.ca.

“We cannot say that eating certain foods will protect your from the coronavirus. They help to produce certain type of components in your body which help fight against infection. They are all interconnected to help boost your immune system.”

In this Wednesday, May 8, 2019 file photo, Britain's Prince Charles and Camilla, Duchess of Cornwall wave from the town hall balcony in Leipzig, Germany. Prince Charles, the heir to the British throne, has tested positive for the new coronavirus. The prince’s Clarence House office reported on Wednesday, March 25, 2020 that the 71-year-old is showing mild symptoms of COVID-19 and is self-isolating at a royal estate in Scotland. It says his wife Camilla has tested negative. (AP Photo/Jens Meyer, File)